Actions for selected content:

Send content to

To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .

To send content items to your Kindle, first ensure no-reply@cambridge.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.

Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

By using this service, you agree that you will only keep articles for personal use, and will not openly distribute them via Dropbox, Google Drive or other file sharing services
Please confirm that you accept the terms of use.

The Late Ordovician tropidodiscid gastropod Alaskadiscus, known only in two areas in Alaska, was named by Rohr, Frýda, and Blodgett (2003). Peter Wagner and Stephen K. Donovan have pointed out to us that the name was previously used for a Cambrian trilobite, Alaskadiscus Zhang, 1980. We propose the new name Alaskodiscus with the same type species, A. donensis Rohr, Frýda and Blodgett, 2003. We feel the similarity in names is not likely to cause undue confusion since the taxa are widely separated by phyla and age.

The spine-bearing Spinicharybdis is placed into a new subfamily Spinicharybdiinae together with Hystricoceras Jahn, 1894. Joint occurrences of genera Beraunia, Coelocaulus, and Morania, as well as members of subfamily Spinicharybdiinae in the gastropod fauna from the Heceta Formation, support its close relationship with gastropod fauna of Bohemia. Additionally, the occurrence of the genus Medfrazyga suggests a faunal link between the Alexander and Farewell terranes of Alaska. Medfrazyga gilmulli n. sp. is the oldest known and the only early Paleozoic member of the family Palaeozygopleuridae.

A small faunule of hypercalcified agelasiid demosponges has been recovered from outcrops of the Silurian Heceta Formation on Prince of Wales Island in southeastern Alaska. Included are abundant Girtyocoeliana epiporata (Rigby and Potter, 1986), of the Girtyocoeliidae Finks and Rigby, 2004; fragments of Alaskaspongiella laminosa n. gen. and sp., Polyplacospongia nodosa n. gen. and sp., and Monolaminospongia gigantia n. gen. and sp., of the Auriculospongiidae Termier and Termier, 1977, and Cladospongia alaskensis n. gen. and sp., Virgulaspongia uniforma n. gen. and sp., and Stipespongia laminata n. gen. and sp. of the Preperonidellidae Finks and Rigby, 2004. Also included are a few fossils of uncertain taxonomic placement, including Turbospongia biperforata n. gen. and sp., along with a small, chambered, tubular fragment and several porous tubular stems that may be additional poriferans. Some isolated octactine-based heteractinid spicules were also recovered from the etched residues.

Study of the oldest macluritid gastropod, Macluritella stantoni Kirk, 1927 from the Lower Ordovician of Colorado, has revealed that its early whorls are openly and dextrally coiled, in contrast to those in later teleoconchs which are sinistrally coiled. This is the first documentation of heterostrophic coiling in members of the Macluritoidea, which have been considered to be dextrally hyperstrophic. Juvenile M. stantoni may be interpreted as dextrally orthostrophic and, thus, it had the same type of soft-body-shell arrangement as the vast majority of living and fossil gastropods. This intepretation also suggests that the Macluritoidea evolved from the dextrally orthostrophic gastropods, and their dextral hyperstrophy is derived and not a primary feature. In addition, occurrence of shell heterostrophy in M. stantoni brings additional evidence that the Macluritoidea and Onychochiloidea are not closely related taxa. Relationships between the Macluritoidea and Euomphaloidea are still uncertain. This study provides the oldest evidence (Early Ordovician) for shell heterostrophy in the class Gastropoda.

Ceratopea Ulrich, 1911, from the Lower Ordovician of North America, Greenland, and Scotland, is one of a few gastropod genera that was established on the calcareous operculum and not the shell. The operculum is commonly found disassociated, and for many years the nature of the shell itself was unknown (Yochelson, 1975). Yochelson and Bridge (1957, pl. 38, figs. 8–9) illustrated an artificial association of C. unguis with its presumed shell made years earlier by Ulrich and Bridge (Yochelson, written commun.). However, the basal part of the shell is not present. Only one life association of the shell and operculum has been previously documented (Yochelson and Wise, 1972), and that shell is incompletely preserved.

Gastropods that occur in the Anomalorthis brachiopod zone in the Spring Inlet Member of the Table Point Formation and in the Orthidiella brachiopod zone of the Shallow Bay Formation of the Cow Head Group are documented. Gastropods from western Newfoundland comprise part of the Toquima-Table Head fauna, and six of the seven genera described here are also found in Whiterockian strata of Nevada. Four species assigned to Monitorella Rohr, 1994, Maclurites Le Sueur, 1818, and Malayaspira Kobayashi, 1958, originally described by E. Billings in 1865 from Middle Ordovician (Whiterockian) strata of Newfoundland are revised. Five species of Helicotoma Salter, 1859, Malayaspira Kobayashi, 1958; Lytospira Koken, 1896; Rossospira Rohr, 1994; and Pachystrophia Perner, 1903, not previously reported from Newfoundland are also described. The probable opercula of Monitorella crenulata (Billings, 1865), and Maclurites emmonsi (Billings, 1865), are also illustrated for the first time.

Fossilized opercula are uncommon in Paleozoic rocks, and shells with the operculum in place are rare. A single specimen with the operculum in place was discovered by P. Slehofer in a concretion in the Ordovician Zahorany Formation of the Prague Basin. Formerly known as Trochonema excavatum Barrande in Perner, 1903, the species is the basis of the new genus Slehoferia. Perner (1903) reported the shell of the same species from two localities, and additional specimens without the operculum are in the collections of the National Museum and Czech Geological Survey. Studied material is deposited in the paleontological collection of the Czech Geological Survey, Prague.

The only two known life associations of the shell and operculum of Maclurites Le Sueur, 1818, are described for the first time. Maclurites cf. magnus Le Sueur, 1818, from the Middle Ordovician of Alaska demonstrates that the operculum fits slightly inside the aperture, and when closed, the operculum extends down below the base of the shell and may have acted as an anchor. The operculum of Maclurites bigsbyi (Hall, 1861), from the Middle Ordovician of Wisconsin, is illustrated for the first time and is confirmed to be distinct from Maclurina logani (Salter, 1859).

Two occurrences of Middle Ordovician opercula belonging to the gastropod Maclurites are described, one from the Taimyr Peninsula, Siberia, and one from the Kuskokwim Mountains, Alaska. The Taimyr opercula are the first to be described from Russia. Like other opercula of the genus, these thick specimens have a relatively massive prong on the interior to which the retractor muscle was attached. The Alaskan specimens preserve a secondary muscle attachment site. The described occurrences of Maclurites opercula are summarized.

Additional Whiterockian gastropods are described from the Antelope Valley Formation of Nevada. A new genus with affinities to Oriostoma is described as well as the new species Clathrospira glindmeyeri, Trochonemella antelopensis, and Raphispira martinensis. The lower ranges of Clathrospira Ulrich in Ulrich and Scofield and Trochonemella Okulitch, the species Liospira americana Billings and Raphistomina lapicida (Salter) are extended to the Whiterockian. The ranges of Raphispira Perner and the family Oriostomatidae Wenz are tentatively extended downward to the Whiterockian.

Several biostratigraphically important gastropod genera are described from Alberta, British Columbia, Yukon Territory, and the District of Mackenzie. Malayaspira is present in the mid-Ibexian Kechika Group. Palliseria, Maclurites, Teiichispira, Malayaspira, Barnesella, and Ceratopea occur in the Skoki Formation (highest Ibexian and lower Whiterockian) and Helicotoma and Palliseria in the Sunblood Formation (lower Whiterockian). The largest known Teiichispira operculum is illustrated. The forms are particularly useful for age determination within relatively narrow limits and most of the taxa are readily identified in the field.

Several unsilicified gastropod specimens were collected by John B. Mertie, Jr., on July 13, 1941, during a boat traverse along the Porcupine River of east-central Alaska. The specimens were originally deposited in the Ulrich (Cambrian and Ordovician) stratigraphic collections of the U.S. Geological Survey at the National Museum of Natural History, Washington, D.C. The collection contains one specimen of Palliseria and three specimens of Maclurites, all of which are broken from the limestone. Despite the lack of much of the shell material, they are easily identified as to genus. One specimen identified as Palliseria is particularly significant.

Gastropods are abundant in the Middle Ordovician (Whiterockian) Antelope Valley Formation of Nevada. Because Whiterockian rocks are absent in much of central and eastern North America, these Nevada gastropods play a significant role in understanding the Early to Middle Ordovician transition of the class. The shell and operculum of a new genus and species of macluritoid, Monitorella auricula, is described. New euomphaloid taxa include Walcottoma frydai n. gen. and sp., Rossospira harrisae n. gen. and sp., Barnesella measuresae n. sp., Helicotoma gubanovi n. sp., Lytospira yochelsoni n. sp., and Malayaspira hintzei n. sp.

The euomphalacean gastropod Lytospira gerulus n. sp. is described from the Middle Ordovician of west-central Alaska. The species is among the oldest known carrier shell specimens, and also shows evidence of repaired shell breakage; the breakage may have been the result of unsuccessful predation attempts. The interior of the shell shows an unusual spiral groove and ridges that may have been associated with the animal's retractor muscle. This internal groove may be an overlooked feature of all species of Lytospira.

The concept of the Ordovician gastropod genus Maclurites Le Sueur, 1818, at present includes much variation. Maclurina Ulrich in Ulrich and Scofield, 1897, is removed as a subjective synonym of Maclurites and reestablished as a separate genus. Species of Maclurites with spiral grooves on the outer whorl surface and a relatively small umbilicus are transferred to Maclurina. Maclurina manitobensis (Whiteaves, 1890) forms a distinctive part of the Late Ordovician-age “Arctic Ordovician fauna.” An unusually large specimen (25 cm in diameter) from the Bighorn Dolomite (Upper Ordovician), Wyoming, is illustrated; this Wyoming specimen is the volumetrically largest Paleozoic gastropod ever reported.

A single specimen of the platyceratacean gastropod Raphispira showing one complete and one incomplete, slightly elliptical borehole was recovered from the Antelope Valley Formation in central Nevada. Circular boreholes may be formed by a variety of causes, but they are most commonly attributed to the predators. In the Paleozoic the holes are most common in brachiopods, both calcareous and phosphatic. This is the oldest reported occurrence in a calcareous shell. In most instances, if a hard-bodied form is consumed by a carnivore, little recognizable evidence remains; therefore, predator boreholes are helpful in determining trophic relationships.

Groomodiscus rossi n. gen. and sp., a bellerophontacean from the Ordovician of Nevada that uncoiled at maturity, is described and placed in the Gastropoda. The deep notch or sinus of the shell is interpreted to have functioned the same as a deep slit, and the new genus is placed within the tropidodiscinids. Uncoiling and thickening of the shell in the mature stage of growth is probably an indication of a fundamental change of life style to a sedentary mode. Fragmentary specimens of the final, uncoiled portion of the whorl resemble the apertural portion of hyoliths. From a functional viewpoint, compressed planispiral shells are concluded more likely to be gastropods than monoplacophorans.

Oriostoma bromidensis n. sp., the oldest reported occurrence of Oriostoma Munier-Chalmas, 1876, is described from the Bromide Formation (Middle Ordovician, Blackriverian) of Oklahoma. The species is also the oldest known representative of the family Oriostomatidae Wenz, 1938. It is one of few gastropods known from the Bromide and is smaller than the widespread and abundant Oriostoma typical of the Silurian.

Two new spine-bearing gastropods, Chlupacispira spinosa n. gen. and sp. and Spinulrichospira cheeneetnukensis n. gen. and sp., are described from the late Early Devonian (Emsian) and early Middle Devonian (Eifelian), respectively, of west-central Alaska. These represent the earliest reported spiny pleurotomariacean gastropods. Otherwise, spinose pleurotomariaceans are known from strata no older than Carboniferous age. Spinulrichospira cheeneetnukensis n. gen. and sp. appears to represent a more highly ornamented derivative of Ulrichospira Donald. Both new genera are part of the more highly ornamented fauna which occurred in warm equatorial waters of the Old World Realm during the Early and Middle Devonian, in contrast to more weakly ornamented shells of the Eastern Americas Realm and even more weakly ornamented (almost totally “plain”) shells of the Malvinokaffric Realm. The latter two realms are thought to represent subtropical to warm temperate and cool temperate to cool polar conditions, respectively.